Not Applicable
Not Applicable
1. Field of the invention
This invention relates to circular saws and particularly to circular saws that can accept a dado cutting blade
2. Description of the Prior Art
Circular saws have been used for many years to cut wood. Typically, these saws are powered, hand-held tools that are used to cut plywood and framing members in construction.
A stationary table saw is typically used in construction and woodworking such as furniture making. A radial arm saw is a circular saw that is mounted on a frame. The saw can be moved on a slide to allow the saw to be pulled through a workpiece. Both the stationary table saw and the radial arm saw cut wood. They also can be used to make special cuts, such as moldings, rabbets and grooves called dados.
Both of these saws have an arbor that extends from the motor. Blades are mounted on this arbor and are held in place with a nut. Most brands of these saws use an arbor that is long enough to accept a dado blade. There are two types of dado blade. The first is called a xe2x80x9cwobblexe2x80x9d blade. This blade uses a pair of eccentric hubs that are secured around a blade. By adjusting the hubs, the blade can be made to xe2x80x9cwobblexe2x80x9d when it is placed on the saw arbor. The wobble causes the blade to cut a groove instead of a straight line in a workpiece. The second type of dado blade is a stacked cutter. Here, a number of chipper blades are placed (or stacked) between two outer saw blades. The number of chipper determines the width of the dado. The blades and chippers are all xe2x85x9 inch thick. Using just the two blades produces a dado of xc2xc inch. By stacking chipper, the dado with can be extended up to one inch.
Although a hand-held circular saw is very similar to the radial arm saw and is related to the stationary table saw, the hand-held devices cannot make these cuts because they are not designed to accept the large thickness blades needed to make them. Hand-held circular saws have small arbors that typically can accept only one blade. Ostensibly, the use of the small arbor is for safety. These saws are often used by inexperienced users. Placing a dado blade on such a saw improperly could be dangerous. However, these saws are capable of cutting with these blades if the blades could be made to fit on the arbor.
One U.S. Patent teaches a system that attempts to do that. U.S. Pat. No. 4,279,280 to Pairis teaches a system that uses an auxiliary shaft to support a stacked dado cutter. In this design, a bushing is secured to the arbor end of the saw. The arbor is removed. An outer shaft is secured to the bushing by a setscrew. A set of dado blade cutters and spacer washers are placed on the outer shaft. A long locking bolt is placed into the outer shaft to secure the blades in place. The bolt is secured by threads in the bushing. An extra-wide guard is placed over the assembly for safety.
There are several problems with this design. First, the design requires modification of the saw by changing the arbor to the bushing. Next, the outer shaft is secured to the bushing by only a setscrew and the long bolt. Finally, the long bolt is secured in the bushing by only a few threads. While it is possible that the blades will rotate when the saw is turned on, it may not remain stable when cutting actual wood. The length of the long bolt is such that a considerable unsupported moment force may be generated at the head of the long bolt. Moreover, overtime, vibration may cause the setscrew to loosen. Because of the forces on the device when in use, the loose setscrew can cause serious problems in the operation of the device.
The instant invention overcomes these difficulties. First, it uses the existing arbor to secure the blades. This eliminates the setscrew and bushing arrangement of the Pairis patent and allows the device to be used with any circular saw. Next, it replaces the saw guard with an extended-width guard. Unlike the guard of Pairis, however, this guard has a bushed bracket that supports the head of the extra-length arbor bolt. Thus, both ends of the bolt are fully supported. This eliminates the unsupported moment on the bolt. Moreover, because no setscrews are used, the effects of vibration are eliminated. With the new system, any type of dado blade can be used with the hand-held circular saw in a safe and efficient manner.
The saw uses an extension arbor, that fits over the existing arbor, to hold a wider dado blade. The extension arbor is held in place by a locking bolt that passes through a bushed brace that is secured to the guard. In this way, both ends of the extension arbor are supported, providing strength and stability of the saw. The saw has a larger base plate and guard to accommodate the wider blades. Any type of standard dado blade may be used with the extension arbor.